Light falls on a non-reflecting surface normally. If the average force exerted on a surface with area 15 ~cm ^2 during 20 minute time interval is 10⁻⁶ ~N , then energy flux of light is (Velocity of light =3 10^8 ~ms ⁻¹ )

Step-by-step solution

Radiation pressure on a totally absorbing (non reflecting) surface is Pressure = F A = I c ...(i) Where, I= Intensity, c= speed of light it is given that, aligned & F=10⁻⁶ ~N & A=15 ~cm ^2=15 10⁻⁴ ~m ^2 aligned Time for which radiation falls on surface continuously, t=20 ~min =20 60 ~s =1200 ~s Speed of light, c=3 10^8 ~m / s From Eq. (i) we have, I= F C A I= 10⁻⁶ 3 10^8 15 10⁻⁴ aligned & =2 10^5 ~W / m ^2 & =20 10^4 ~W / m ^2 aligned